The present invention relates to a structural composite material. More particularly, the present invention provides a foam core/ fiber-reinforced structural composite material. The invention further provides a method for manufacturing the composite and a boat structure made from the material.
To date, a wide variety of structural composite materials have been developed. Generally, such materials are formed by laminating either a thermoplastic or thermoset skin to one or both sides of a rigid foam core. Structural composites find use in applications where light weight, strength, surface finish and economy are important such as, for example in the automotive, aircraft and boat building industries.
In the case of structural members formed from thermoplastic/foam composites, strength and stiffness are provided by incorporating a rib or other framing member at strategic points within the structural member. Depending on the function of the structural member and the specifications it must meet, such an approach may be impracticable or impossible.
Prior art thermoplastic/foam composites also present a number of problems associated with the thermoplastic skin that covers the foam core. Generally, the thermoplastic surfaces of such composites are soft and easily scratched; they exhibit low gloss, poor weatherability and problems with adhesion are frequently encountered. For example, thermoplastic skins formed from ABS exhibit poor weatherability, embrittle quickly and show a sharp decline in impact resistance over time. Such a surface would quickly fail if used, for example, as the outer surface of a boat.
Thermoplastic skins formed from an EPDM-rubber modified styrene-acrylonitrile copolymer (hereinafter AES thermoplastic) eliminate some of these problems. AES thermoplastic exhibits better weatherability, chemical resistance and impact resistance than ABS. However, the problems of overall strength and rigidity discussed above are not mitigated by the use of AES.
Fiber-reinforced foam composites offer improved strength and rigidity compared with thermoplastic/foam composites. Fiber-reinforced foam composites are commonly manufactured by molding a foam core and, after the foam core has cured, laminating a fiber-reinforced resin layer to the core's surface. The prior art is limited to manual, open mold processes for laminating the fiber-reinforced resin layer to the foam core. Generally, the foam core is covered with a layer of fibrous material, and a thermoplastic or thermoset resin is applied by hand or by spraying. The resin impregnates the fibrous material and penetrates into the foam. Once the resin cures and hardens, a fiber-reinforced resin layer is firmly bonded to the foam core.
Prior art methods of manufacturing fiber-reinforced foam composites present several important disadvantages. First, a uniform layer of the fiber-reinforced resin cannot be obtained when the resin is applied manually or by spraying. Thus, the final product lacks consistency in thickness, density and resin content. Such inconsistencies can cause localized areas of reduced strength in structural members made from the composite. Moreover, the difficulties associated with mating structural members having non-uniform thickness must be addressed. Foam/resin delamination also frequently occurs in areas of the composite where the resin content is low or completely absent.
Second, the hand lay-up or hand spray-up methods taught by the prior art result in the emission of significant quantities of chemicals into the work place. For example, such methods often involve the use of styrene, a substance which OSHA and a number of other health organizations are currently investigating as a possible carcinogen. In the light of the potential hazards associated with styrene, OSHA has issued a proposed regulation which limits the level of free styrene in the work place to 50ppm. A recent study concluded that compliance with OSHA's proposed regulation would cost open molders in the reinforced plastics industry $1.6 billion. In addition, the study projects that the annual operating cost of maintaining this safety level would be $500 million.
Co-pending patent application, filed Jul. 21, 1989, assigned Ser. No. 383,811 and naming the above-named inventor, discloses a thermoplastic/foam core/fiber-reinforced thermoset resin composite manufactured in a closed mold process. The composite is manufactured by forming a thermoplastic layer, applying a foam core to one surface of the thermoplastic layer and then laminating a fiber-reinforced thermoset resin to the foam core in a resin transfer molding process. This method of manufacture significantly reduces the emission of chemicals and produces a final product having uniform thickness, density and resin content. However, where the method is employed to produce large structural members, a substantial clamping force must be applied to the matched die mold in which the resin transfer molding process is carried out to ensure that tolerances are maintained. Clamping devices capable of exerting the required forces are expensive and not generally available to molders operating small shops.
It is, therefore, an object of the present invention to provide a process for making a foam core/fiber-reinforced structural composite that significantly reduces the free air emissions of hazardous chemicals such as styrene.
It is a further aim of the invention to provide a method for manufacturing such a composite that molders throughout the reinforced plastics industry will find economical.
It is a still further aim of the invention to provide a foam core/fiber-reinforced resin composite having controlled uniformity of thickness, density and resin content.
It is a further aim of the invention to provide a foam core/fiber-reinforced resin composite having a highly cosmetic, impact resistant, chemical resistant and weatherable surface.
It is a still further aim of the invention to provide a boat structure made from such a composite.